1. Field
An embodiment or embodiments relates to a fusing device and an image forming apparatus, and more particularly, to a fusing device and an image forming apparatus using the same by which characteristics of compression/separation (or decompression) of a fusing roller by/from a compression roller may be improved.
2. Description of the Related Art
An image forming apparatus, such as a photocopier, a printer, or a fax, may form a toner image on an image receptor based on image information, transfer the toner image onto a recording material, allow the recording material on which the toner image is received to pass through a fusing device, and fuse the toner image to the recording material through heat and pressure. In general, the fusing device may be a thermal-roller type or a belt (or film) type.
A thermal-roller-type fusing device may include a fusing roller and a compression roller, and the fusing roller may heat itself, as shown in Japanese Patent Publication No. 2005-326524. Meanwhile, a belt-type fusing device may include a fusing roller and a compression roller, and a heated belt may be supplied to the fusing roller, as discussed in Japanese Patent Publication No. 2009-237188. In an ordinary operation state, the compression roller may be compressed against the fusing roller by a compression spring and rotate. Also, when a recording material on which a toner image is received is allowed to pass through the compressed rollers, the toner image may melt due to heat of the fusing roller (or belt) and be fused to the recording material.
However, when the compression roller remains compressed against the fusing roller for a long time in a stop state, the rollers may be deformed or the belt may be damaged. Accordingly, for example, when the stop state is maintained for a long time, when the recording material is jammed, or when the fusing roller is rapidly heated, the compression roller may be separated from the fusing roller against an elastic pressure of a compression spring.
In general, compression/separation of the fusing roller by/from the compression roller may be enabled by a simple lever mechanism using a cam, as shown in Japanese Patent Publication No. 2005-326524 and Japanese Patent Publication No. 2009-237188. The simple lever mechanism may include a compression lever configured to sustain the compression roller, a compression spring configured to elastically compress the compression roller against the fusing roller using the compression lever, and the cam configured to operate the compression lever. In the simple lever mechanism, the compression lever may be moved toward the fusing roller or separated from the fusing roller due to rotation of the cam so that the compression roller may be compressed against or separated from the fusing roller.
However, high speed formation of an image and formation of a high-definition image require a fusing nip having a great width in a conveyance direction of the recording material to ensure a time taken for the fusing roller to fuse the toner image to the recording material. Accordingly, a sufficient distance over which the compression roller is compressed against and separated from the fusing roller should be ensured.
Therefore, a conventional fusing device increases a distance over which a compression roller operates by increasing an operation radius (corresponding to a difference between a maximum radius and a minimum radius) of a cam or increasing a lever ratio. However, a space containing the cam or the compression lever may be increased, thus increasing the size of not only the fusing device but also that of an image forming apparatus.